There were no science degrees or science Fellows, Lecturers or Professors in Cambridge before the mid 1800s; prior to the invention of the Natural Sciences degree in 1851 any study of Biology was undertaken as a hobby.
There were probably many early natural historians; the first of note seems to have been William Vernon who matriculated at Peterhouse in 1685, becoming a Fellow in 1692. As a student Vernon collected mosses and butterflies. These were not minor hobbies, for the butterflies are historically important and the plant specimens he collected were used by his friend John Ray in compiling 'Synopsis Stirpium Brittanicum', one of the earliest texts upon which modern taxonomy is founded. These include stinking goosefoot Chenopodium vulvaria ('olidum') collected 'under the wall that joynes to Peter-house Tennis-court'. The butterflies include the first British collections of the Bath white Pontia daplidice (which may also be the world's oldest pinned insect specimen), Queen of Spain fritillary Issoria lathonia, clouded yellow Colias edusa (collected along with Ray), Duke of Burgundy fritillary Hamearis lucina and wood tiger moth Parasemia plantaginis.
In 1698 Vernon was granted leave to absent the college for four years to travel to the new colony of Virginia "to improve Natural Phylosophy particularly ye discovery of American Mosses & Butterflies". He later planned to collect in the Canary islands but was unable to find a boat and collected in Kent instead! In recognition of his contributions to natural history he was elected a Fellow of the Royal Society in 1702 (although he never took up the fellowship).
Vernon sometimes collected plants with other Petreans, including Richard Davies (matriculated 1694, Fellow 1699-1702) in Virginia and Robert Antrobus (matriculated 1699, Fellow 1704) was regarded as a protege of Vernon and maintained a life-long interest in natural history. When a Master at Eton he passed on this interest to his nephew and pupil Thomas Gray. Gray himself matriculated at Peterhouse in 1734. Gray was noted as the foremost English-language poet of the time and was offered the post of Poet Laureate in 1757. Today his fame rests on his poem 'Elegy Written in Country Church' which owes much to his interests in nature.
Further botanists followed, with Hugh Davies (1748, Fellow 1763) who whilst being the rector of Aber published 'Welsh Botanology' in 1813 and edited 'Pennant's Indian Zoology'. Charles Lyell (1791), father of the famous geologist of the same name kept up the college's tradition of amateur moss enthusiasts (although also including lichens). William Bingley (1795) combined amateur botany with being Deacon of York. He was of some note at the time, being a Fellow of the Linnean Society and author of several now forgotten books: 'Animal Biography or Anecdotes of the Animal Creation', 'Memoirs of British Quadrupeds', 'Practical Introduction to Botany' and 'Animated Nature'. (p align="justify">John Hogg (1818, Fellow 1827) seems to have been Peterhouse's second Fellow of the Royal Society with a biological interest. He combined observations of botany, fish, birds and geology in studies of the natural history of Tyneside and also published on Sicilian plants. Geology also attracted two Petreans who later became tutors of William Thomson (later the great physicist Lord Kelvin): William Hopkins (1827) and Henry Wilkinson Cookson (1828), five-times Vice Chancellor.
Although Chemistry had its first Professorship in 1702, Physics (as 'Natural Philosophy') in 1707 and Botany in 1728 (there was no Professor of Zoology until 1866 despite the creation of the University Museum of Zoology 50 years earlier), distinct sciences were of little meaning until the appearance of people such as Kelvin. At this time biology also was becoming recognisably more technical than the earlier 'natural philosophy'. In 1843 a Peterhouse student George Kemp gave a paper to the Cambridge Philosophical Society on the subject of bile; modern physiology had arrived. These changes were recognised by the University with the creation of the Natural Sciences Tripos in 1851. It took another 12 years for the colleges to fully embrace the new degree and to start to offer scholarships to exceptionally able students. In 1868 Peterhouse became the 5th college to offer NatSci scholarships.
One of Peterhouse's first NatSci students was Herbert Mills Birdwood (1854), achieving a First in 1858 (and a Fellowship). He went on to be an administrator in British India where he used his degree to write on the Indian flora (maintaining Peterhouse's botany tradition). Neville Goodman (Fellow-Commoner 1862) made insect collections, mainly in South America. Some of Goodman's Amazon and South African butterfly collections were given to the Museum of Zoology and Comparative Anatomy (now the University Museum of Zoology, Cambridge) in 1890. At the time these made up most of the non-British insects in the collection. His observations of mimicry contributed to the discussions of evolution and were cited by Wallace in his book on 'Darwinism'.
Other Petreans who corresponded with Charles Darwin and provided observations they made when posted overseas in colonial or missionary roles include Samuel Owen Glenie (1829). Peterhouse's first Scholar in Natural Sciences was William Stone (1875, awarded a Scholarship in Botany in 1878). He later became a lawyer but retained an interest in biology, being an occasional Lecturer in Botany at Newnham College and becoming a Fellow of the Linnean, Zoological and Royal Geographical Societies. He was something of an adventurer, traveling up the White Nile in 1882, and being present at the coronation of Czar Nicholas II. He was one of the college's most significant benefactors.
The college's first professional biologist was Michael Cresse Potter (1877) who became University Lecturer in Botany in 1883 and Curator of the University Herbarium. He studied algae growing on terrapins in Portugal in 1886 and collected plants in Sri Lanka in 1888-9. Potter became head of the Botany Department at Durham in 1889. As well as writing undergraduate botany texts, in his later years he moved on to investigate electrical physiology in metabolism. These ideas led to development of microbial batteries 100 years later.
Peterhouse's early preeminence in botany gave way to zoology in the late 19th century. Walter Ambrose Heath Harding (1889) joined the colonial administration in India where he contributed to the knowledge of the zoology of the region, most notably writing the leeches volume of the Fauna of British India. He made a significant bequest to the support of the Cambridge University Lectureship in Zoology which his father had established. He was a Fellow of the Linnean and Zoological Societies.
Sir John William Sutton Pringle was the college's first professional zoologist, joining the college as a Fellow and University Lecturer in zoology in 1945. His interest were in insect physiology and in 1959 he became Reader in Experimental Cytology, before moving to a Professorship in Oxford in 1961. He was elected a Fellow of the Royal Society in 1954 in recognition to his work on insect flight muscles and cicada song.
Another FRS physiologist was Richard Darwin Keynes (Fellow 1952), who worked on neurophysiology, including demonstration of how electric fish generate electric currents. John Fincham (1944, Bye-Fellow 1949) was a pioneer of microbial genetics and was appointed to a string of lectureships and professorships in botany and genetics in Leicester, Leeds and Edinburgh, before being appointed the Arthur Balfour Professor of Genetics in Cambridge (1984-91).